U.S. patent number 4,479,471 [Application Number 06/491,208] was granted by the patent office on 1984-10-30 for method for controlling engine idling rpm immediately after the start of the engine.
This patent grant is currently assigned to Honda Motor Co., Ltd.. Invention is credited to Shumpei Hasegawa, Noriyuki Kishi, Takashi Koumura.
United States Patent |
4,479,471 |
Hasegawa , et al. |
October 30, 1984 |
Method for controlling engine idling rpm immediately after the
start of the engine
Abstract
An idling rpm control method for feedback control of a control
valve for controlling the quantity of supplementary air being
supplied to the engine in response to a difference between actual
engine idling rpm and desired idling rpm. At the start of the
engine, the control valve is continuously opened for a
predetermined period of time from the time the engine rpm has
increased above a predetermined value lower than the desired idling
rpm, thereby maintaining the engine rpm at a value higher than the
above desired idling rpm. The above predetermined period of time
may desirably be set to a value as a function of engine
temperature, preferably detected immediately after the engine rpm
has exceeded the above predetermined value of engine rpm.
Inventors: |
Hasegawa; Shumpei (Niiza,
JP), Kishi; Noriyuki (Itabashi, JP),
Koumura; Takashi (Iruma, JP) |
Assignee: |
Honda Motor Co., Ltd. (Tokyo,
JP)
|
Family
ID: |
13628605 |
Appl.
No.: |
06/491,208 |
Filed: |
May 3, 1983 |
Foreign Application Priority Data
|
|
|
|
|
May 8, 1982 [JP] |
|
|
57-77250 |
|
Current U.S.
Class: |
123/339.22;
123/588 |
Current CPC
Class: |
F02D
31/005 (20130101); F02D 41/061 (20130101); F02D
2011/102 (20130101) |
Current International
Class: |
F02D
31/00 (20060101); F02D 41/06 (20060101); F02D
009/02 (); F02D 031/00 () |
Field of
Search: |
;123/179G,339,585,588 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Argenbright; Tony M.
Attorney, Agent or Firm: Lessler; Arthur L.
Claims
What is claimed is:
1. A method for controlling a control valve for regulating the
quantity of supplementary air being supplied to an internal
combustion engine, in a feedback manner responsive to the
difference between actual engine rpm and desired idling rpm during
idling of the engine, the method comprising the steps of: (a)
detecting engine rpm at the start of the engine; and (b) opening
said control valve to a maximum opening for a predetermined period
of time from the time the engine rpm is detected to have increased
above a predetermined value lower than said desired idling rpm,
whereby the engine rpm is maintained at a value higher than said
desired idling rpm.
2. A method as claimed in claim 1, including the step of setting
said predetermined period of time to values as a function of the
temperature of the engine.
3. A method as claimed in claim 2, including the step of detecting
the temperature of the engine immediately after the engine rpm has
increased above said predetermined value of engine rpm.
4. A method as claimed in claim 2, wherein said predetermined
period of time is set to larger values as the temperature of the
engine decreases below a predetermined value and further becomes
lower.
5. A method as claimed in claim 2, wherein said predetermined
period of time is set to larger values as the temperature of the
engine increases above a predetermined value and further becomes
higher.
Description
BACKGROUND OF THE INVENTION
This invention relates to an idling rpm feedback control method for
internal combustion engines, and more particularly to such method
which allows the engine to perform stable idling operation
immediately after the start of same.
In an internal combustion engine, the engine can easily stall due
to a drop in the engine speed when the engine is operated in an
idling condition at a low temperature of the engine cooling water
or when the engine is heavily loaded with loads by head lamps, air
conditioner, etc. in a vehicle equipped with the engine. To
eliminate such disadvantage, an idling rpm feedback control method
has been proposed e.g. by Japanese Patent Provisional Publication
(Kokai) No. 55-98628, which comprises setting desired idling rpm in
dependence upon engine load of the engine, detecting the difference
between actual engine rpm and the desired idling rpm, and supplying
a quantity of supplementary air to the engine in a manner
responsive to the detected difference so as to minimize the same
difference, to thereby control the engine rpm to the desired idling
rpm.
Even if such idling rpm control method is applied, it is difficult
to ensure complete combustion of the air/fuel mixture within the
combustion chambers of the engine at or immediately after the start
of the engine, especially in cold weather, due to low engine
temperature, particularly, low temperature of the wall surfaces of
the combustion chambers, causing unstable rotation of the engine at
engine idle immediately following the start of the engine. Further,
since immediately after the start of the engine the battery
installed in the engine is charged by the dynamo or generator as it
is used for actuating the starter during engine cranking, and the
operating dynamo forms a heavy load on the engine, thereby further
making the engine operation unstable.
On the other hand, when the engine is started while it has a high
temperature, for instance, when it is restarted immediately after
operation in hot weather, there can occur bubbles in pipes of the
fuel feeding system of the engine due to high temperature. The
presence of such bubbles also can result in very unstable rotation
of the engine at engine idle, requiring prompt removal of such
bubbles.
SUMMARY OF THE INVENTION
It is the object of the invention to provide an idling rpm control
method which is adapted to maintain the engine rpm at a value
higher than desired idling rpm for a predetermined period of time
at engine idle immediately following the start of the engine,
thereby ensuring highly stable idling operation of the engine.
The present invention provides an idling rpm feedback control
method for controlling a control valve for regulating the quantity
of supplementary air being supplied to an internal combustion
engine, in a feedback manner responsive to the difference between
actual engine rpm and desired idling rpm during idling of the
engine. The method of the invention is characterized by the steps
of: (a) detecting engine rpm at the start of the engine; and (b)
opening the above control valve to a maximum opening for a
predetermined period of time from the time the engine rpm is first
detected to have increased above a predetermined value lower than
the above desired idling rpm, whereby the engine rpm is maintained
at a value higher than the desired idling rpm.
Preferably, the above predetermined period of time is set to a
value as a function of the temperature of the engine, which is
detected immediately after the engine rpm has increased above the
above predetermined value. Preferably, the predetermined period of
time is determined in either of the following manners: (i) setting
the predetermined period of time to larger values as the engine
temperature decreases below a predetermined value and further
becomes lower; and (ii) setting the predetermined period of time to
larger values as the engine temperature increases above a
predetermined value and further becomes higher.
The above and other objects, features and advantages of the
invention will be more apparent from the ensuing detailed
description taken in conjunction with the accompanying
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a block diagram illustrating the whole arrangement of an
idling rpm control system to which is applicable the method of the
present invention;
FIG. 2 is a timing chart showing a manner of supplying the
supplementary air to the engine in synchronism with generation of
pulses of an engine top-dead-center (TDC) signal;
FIG. 3 is a timing chart showing a manner of detecting a parameter
indicative of the intake air quantity;
FIG. 4 is a timing chart showing a manner of detecting the intake
air quantity parameter with time intervals optionally
determined;
FIG. 5 is a timing chart showing a manner of supplying the
supplementary air with a time delay with respect to generation of
pulses of the TDC signal;
FIGS 6a, 6b, and 6c are a flow chart showing a program for
performing an idling rpm control method by means of a first control
valve, executed within an electronic control unit (ECU) in FIG.
1;
FIG. 7 is a timing chart showing a manner of control of the first
control valve in decelerating mode and in feedback mode;
FIG. 8 is a graph showing, by way of example, the relationship
between the duty factor for the valve opening period of the first
control valve in decelerating mode and the engine rpm;
FIG. 9 is a timing chart showing a manner of control of the first
control valve in accelerating mode;
FIG. 10 is a flow chart showing a manner of setting the desired
idling rpm;
FIG. 11 is a graph showing the relationship between the engine
cooling water temperature and a value MTW proportional to the
reciprocal of the desired idling rpm dependent upon the engine
cooling water temperature;
FIGS. 12a, 12b, and 12c are a timing chart showing a manner of
control of the first control valve applicable when an electrical
load is applied on the engine during feedback control of the engine
rpm at engine idle;
FIG. 13 is a flow chart showing a routine for calculating an
electrical load term DE of the duty factor DOUT for the valve
opening period of the first control valve, executed within the ECU
in FIG. 1;
FIG. 14 is a flow chart showing a routine for calculating a
feedback control term DPIn of the duty factor DOUT for the valve
opening period of the first control valve, applicable during
feedback mode control, executed within the ECU in FIG. 1;
FIGS. 15a, 15b, and 15c are a timing chart showing a manner of
control of the first control valve, applicable when an electrical
load is applied on the engine during deceleration of the engine
with the throttle valve fully closed, wherein the engine rpm
decreases toward the feedback control region; FIGS. 16a, 16b, and
16c are a timing chart showing a manner of the first control valve,
applicable when an electrical load is applied on the engine during
acceleration of the engine wherein the engine rpm increases from
the idling rpm feedback control region;
FIGS. 17a-g are a timing chart showing a manner of controlling the
fuel quantity, applicable when a load such as an electrical load is
applied on the engine during engine rpm control;
FIG. 18 is a graph showing the relationship between a period of
time for which the first control valve continues to be fully opened
from termination of the engine cranking to thereby supply a maximum
amount of supplementary air to the engine, and the engine cooling
water temperature which determines the same period;
FIGS. 19, 19A and 19B are a circuit diagram illustrating an
electrical circuit within the ECU in FIG. 1; and
FIG. 20 is a timing chart showing the timing relationship between
pulses of the TDC signal and the valve opening of the first control
valve.
DETAILED DESCRIPTION
The method of the invention will be described in detail with
reference to the accompanying drawings.
Referring first to FIG. 1, an idling rpm feedback control system is
schematically illustrated, to which is applicable the method of the
invention. In FIG. 1, reference numeral 1 designates an internal
combustion engine which may be a four-cylinder type, and to which
are connected an intake pipe 3 with an air cleaner mounted at its
open end and an exhaust pipe 4, at an intake side and at an exhaust
side of the engine 1, respectively. A throttle valve 5 is arranged
within the intake pipe 3, and a first air passage 8 and a second
air passage 26 open at their open ends 8a and 26a in the intake
pipe 3 at locations downstream of the throttle valve 5 and
communicate at the other ends with the atmosphere. An air cleaner 7
is mounted at the other end of the first air passage 8. Arranged
across the first air passage 8 is a first supplementary air
quantity control valve (hereinafter merely called "the first
control valve") 6 which controls the quantity of supplementary air
being supplied to the engine 1 through the first air passage 8.
This first control valve 6 is a normally closed type and comprises
a solenoid 6a and a valve body 6b disposed to open the first air
passage 8 when the solenoid 6a is energized. The solenoid 6a is
electrically connected to an electronic control unit (hereinafter
called "the ECU") 9.
A third air passage 27 branches off from the second air passage 26,
both of which have their atmosphere-opening ends provided with air
cleaners 28 and 29. Second and third supplementary air control
valves 30 and 31 are arranged, respectively, across a portion of
the second air passage 26 between the junction of the same passage
26 with the third air passage 27 and its atmosphere-opening end and
across the third air passage 27. The control valves 30, 31 are both
a normally closed type and each comprise a solenoid 30a, 31a, and a
valve body 30b, 31b disposed to open the corresponding air passage
when the solenoid 30a, 31a is energized. The solenoids 30a, 30b
have their one ends grounded and the other ends connected to a
direct current power source 24, respectively, by way of switches 15
and 16, and directly to the ECU 9.
Connected to the above first air passage 8 is a branch passage 32
branching off therefrom at a location downstream of the first
control valve 6, which has an end communicating with the atmosphere
and provided with an air cleaner 33, and traversed by a fast idling
control device 34. The fast idling control device 34 is comprised,
for instance, of a valve body 34a disposed to be urged against its
valve seat 34b by a spring 34c for closing the branch passage 32, a
sensor means 34d adapted to stretch or contract its arm 34d' in
response to the engine cooling water temperature, and a lever 34e
pivotable in response to the stretching and contracting action of
the arm 34d' of the sensor means 34d for displacing the valve body
34a so as to open or close the branch passage 32.
A fuel injection valve 10 is arranged in a manner projected into
the interior of the intake pipe 3 at a location between the engine
1 and the open ends 8a and 26a of the first and second air passages
8, 26 opening in the intake pipe 3. The injection valve 10 is
connected to a fuel pump, not shown, and also electrically
connected to the ECU 9.
A throttle valve opening sensor 17 is mounted on the throttle valve
5, and an absolute pressure sensor 12 communicates with the intake
pipe 3 through a conduit 11 at a location downstream of the open
ends 8a, 26a of the first and second air passages 8, 26, while an
engine cooling water temperature sensor 13 for detecting the engine
cooling water temperature as representing the engine temperature,
and an engine rpm sensor 14 are both mounted on the body of the
engine 1. All the sensors and other sensors 25 for detecting other
parameters of the operating conditions of the engine 1 are
electrically connected to the ECU 9.
In FIG. 1, reference numerals 18, 19 and 20 designate electrical
devices such as head lamps, a brake lamp and a radiator cooling
fan, which are electrically connected to the ECU 9 by way of
respective switches 21, 22 and 23. Reference numeral 25 denotes
other engine parameter sensors such as an atmospheric pressure
sensor, which are also electrically connected to the ECU 9.
The idling rpm feedback control system constructed as above
operates as follows: The switch 15 is disposed for turning on and
off in unison with a power switch, not shown, for actuating the air
conditioner, not shown, and therefore when closed, its closing
signal is supplied to the ECU as a signal indicative of an on-state
of the air conditioner in the ECU 9. The closing of the switch 15
causes energization of the solenoid 30a of the second control valve
30 to open the valve body 30b for supplying the engine 1 with a
predetermined quantity of supplementary air corresponding to an
increase in the engine load caused by the operation of the air
conditioner. The switch 16 is mounted, e.g. on a shift lever, not
shown, if the present system is installed in an internal combustion
engine equipped with an automatic transmission, and it is closed
when the shift lever is moved to an engaging position of the
automatic transmission, and supplies an on-state signal indicative
of the engagement of the automatic transmission (hereinafter called
"the D-range signal") to the ECU 9, and the closing of the switch
16 causes energization of the solenoid 31a of the third control
valve 31 to open the valve body 31b for supplying the engine 1 with
a predetermined quantity of supplementary air corresponding to
increased engine load caused by the operation of the automatic
transmission.
Thus, accurate control of the engine rpm can be achieved with ease
due to the provision of the second and third control valves for
supplying supplementary air to the engine 1 in quantities
corresponding to mechanical loads, which are relatively large,
applied by mechanical equipments directly driven by the engine,
such as the air conditioner and the automatic transmission.
The fast idling control device 34 is adapted to operate when the
engine cooling water temperature is lower than a predetermined
value (e.g. 20.degree. C.) such as at the start of the engine in
cold weather. More specifically, the sensor means 34d stretches or
contracts its arm 34d'in response to the engine cooling water
temperature. This sensor means 34d may comprise any suitable
sensing means, such as wax filled within a casing, which is
thermally expandable. When the engine cooling water temperature is
lower than the above predetermined value, the arm 34d' is in a
contracted state, with the lever 34e biased by the force of the
spring 34f in such a position to displace the valve body 34a in a
rightward direction against the force of the spring 34c whereby the
branch passage 32 is opened. Since the opened branch passage 32
allows supply of a sufficient amount of supplementary air to the
engine through the filter 33 and the passages 32, 8, the engine rpm
can be maintained at a higher value than normal idling rpm, thereby
ensuring stable idling operation of the engine without the
possibility of engine stall even in cold weather. Therefore, when
the fast idling control device 34 is operative, the supply of
supplementary air through the first control valve 6, hereinafter
described, is not necessary in addition to that effected through
the fast idling control device 34. Thus, the first control valve 6
is kept inoperative until the engine cooling water temperature
becomes higher than a predetermined value except for a
predetermined period of time immediately after the start of the
engine, hereinafter referred to.
As the arm 34d' of the sensor means 34d is stretched with an
increase in the engine cooling water temperature, it pushes the
lever 34e upward to rotate same in a clockwise direction. Then, the
valve body 34a becomes moved leftward as viewed in FIG. 1, rather
by the force of the spring 34c. When the engine cooling water
temperature exceeds the predetermined value, the valve body 34a
comes into urging contact with the valve seat 34b to close the
branch passage 32, thereby interrupting the supply of supplementary
air through the fast idling control device 34.
The above fast idling control device may have another arrangement
other than the illustrated one, so far as it can increase the
intake air quantity being supplied to the engine 1 so as to
maintain the engine rpm at a value higher than normal idling rpm at
engine idle, when the engine cooling water temperature is lower
than a predetermined value. For instance, it may be adapted to
force the throttle valve to open to a certain opening.
On the other hand, the first control valve 6 is used for feedback
control of the supplementary air quantity wherein the same quantity
is varied so as to maintain the engine rpm at desired idling rpm.
Also, it is used for increasing the supplementary air by a
predetermined amount corresponding to electrical load on the
engine, which is relatively small, when an electrical equipment
such as headlamps, a brake lamp and a radiator cooling fan is
switched on.
The ECU 9 determines the operating conditions and loaded conditions
of the engine 1 in dependence on values of signals indicative of
engine operating condition parameters supplied from the throttle
valve opening sensor 17, the absolute pressure sensor 12, the
engine cooling water temperature sensor 13, the engine rpm sensor
14, and the other engine operation parameter sensors 25, signals
indicative of electrical loads from the electrical devices 18, 19,
20, an on-state signal from the air conditioner, and the D-range
signal from the automatic transmission. The ECU 9 calculates a
desired quantity of fuel to be supplied to the engine 1, that is, a
desired valve opening period of the fuel injection valve 10, and
also a desired quantity of supplementary air to be supplied to the
engine 1, that is, a desired valve opening period of the first
control valve 6, on the basis of the determined operating
conditions of the engine and electrical loads on the engine, and
then supplies driving pulses corresponding to the calculated values
to the fuel injection valve 10 and the first control valve 6. The
valve opening period of the first control valve 6 is determined by
the ratio of the on-state period to the pulse separation of a pulse
signal synchronous with the rotation of the engine 1, e.g. a pulse
signal having each pulse generated at a predetermined crank angle
of the engine 1 (hereinafter called "duty ratio").
The first control valve 6 has its solenoid 6a energized by each of
its driving pulses to open the first air passage 8 for a period of
time corresponding to its calculated valve opening period so that a
quantity of supplementary air corresponding to the calculated valve
opening value is supplied to the engine through the first air
passage 8 and the intake pipe 3.
The fuel injection valve 10 is energized by each of its driving
pulses to open for a period of time corresponding to its calculated
valve opening period value to inject fuel into the intake pipe 3 so
as to achieve a desired air-fuel ratio of the mixture being
supplied to the engine 1. As described in detail later, the valve
opening period of the fuel injection valve 10 is increased or
decreased by a predetermined amount a predetermined number of times
in dependence on electrical load signals from the electrical
devices 18, 19 and 20, on-state signal from the air conditioner,
and the D-range signal from the automatic transmission, and after
the lapse of a predetermined period of time from the inputting of
these signals to the ECU 9, thereby compensating for lag of the
detection of the supplementary air quantity to ensure supply of an
appropriate amount of fuel corresponding to a change in the
supplementary air quantity to the engine 1.
Next, a basic manner of supplying the supplementary air through the
first control valve 6 will now be described with reference to FIGS.
2 through 5. Referring first to FIG. 2, the first control valve 6
is opened in synchronism with generation of each pulse of the TDC
signal at each suction stroke of each cylinder of the engine. It
should be noted that according to the manner shown in FIG. 2, the
first control valve 6 is opened only one time each time a pulse of
the TDC signal is generated, that is, each time the engine goes
through each suction stroke. This manner reduces the frequency of
opening and closing the first control valve to thereby lengthen the
effective life of the first control valve 6.
FIG. 3 shows a manner of detecting absolute pressure in the intake
pipe of the engine as a parameter representative of the total
quantity of suction air being supplied to the engine, which is also
applicable to the system of the invention, and FIG. 4 shows a
manner of detecting the intake pipe absolute pressure at a constant
time interval optionally selected, irrespective of fluctuations in
the intake pipe absolute pressure. According to the manner of FIG.
4, the intake pipe absolute pressure is detected in synchronism
with generation of a sampling signal having a constant pulse
repetition period. The sampling signal cannot correspond in phase
to fluctuations in the intake pipe absolute pressure, making it
impossible to detect a central value of the intake pipe absolute
pressure which is correctly indicative of the actual total quantity
of the suction air. On the other hand, if the first control valve 6
is operated in synchronism with generation of the TDC signal for
controlling the supply of supplementary air, as shown in FIG. 2,
the fluctuations of the intake pipe absolute pressure nearly
correspond in repetition period to the TDC signal, as shown in FIG.
3. Taking this fact into account, the intake pipe absolute pressure
should be detected in synchronism with generation of the TDC
signal, that is, at a substantially constant phase point of the
fluctuation waves of the intake pipe absolute pressure, thus
obtaining central values of the same pressure exactly corresponding
to actual total suction air quantities. In this way, proper amounts
of fuel can be supplied to the engine, which exactly correspond to
actual total suction air quantities, preventing unstable idling
operation of the engine which would otherwise be caused by
fluctuations in the fuel supply quantity.
Further, when supplementary air is supplied to the engine, the
cycle of fluctuations of the intake pipe absolute pressure can
deviate in phase from generation of pulses of the TDC signal,
depending upon the timing of initiation of the opening of the first
control valve 6, that is, the timing of initiation of the supply of
supplementary air, which causes variations in the timing of
obtaining central values of the intake pipe absolute pressure
exactly corresponding to the total suction air quantities. If the
intake pipe absolute pressure is detected always at a constant time
with respect to generation of the TDC signal pulses, irrespective
of such phase deviation of the fluctuations of the intake pipe
absolute pressure, actually detected values of the intake pipe
absolute pressure can be higher or lower than respective central
values of same, due to the above phase deviation. FIG. 5 shows
manners of detecting the intake pipe absolute pressure, in which
the same pressure is detected just upon generation of each pulse of
the TDC signal. According to the engine to which the manners of
FIG. 5 are applied, if the first control valve 6 is opened upon a
lapse of an optional period of time TDLY C after generation of each
TDC signal pulse as shown in the example C in FIG. 5, the resulting
detected value of the intake pipe absolute pressure is higher than
the actual central value, and as a consequence the system judges
that suction air has been supplied to the engine in more quantities
than the actual quantities, and accordingly supplies the engine
with larger quantities of fuel than actually required, resulting in
a too rich mixture being supplied to the engine. On the contrary,
if the first control valve 6 is opened immediately upon generation
of each TDC signal pulse as in the example A, the resulting
detected value of the intake pipe absolute pressure is lower than
the actual central value, resulting in a too lean mixture being
supplied to the engine. In view of the above disadvantages, as
shown in the example B in FIG. 5, the value of a predetermined
delay coefficient should be determined in dependence upon the
configuration of the intake pipe of the engine applied, and the
timing of opening of the first control valve 6, i.e. the timing of
supply of supplementary air should be delayed by a period of time
TDLY B corresponding to the determined coefficient value with
respect to generation of each TDC signal pulse so as to always make
the phase of the fluctuating cycle of the intake pipe absolute
pressure constant relative to the timing of generation of the TDC
signal pulses, thus making it possible to positively detect central
values of the absolute pressure. In this manner, fuel can be always
supplied to the engine in proper quantities exactly corresponding
to quantities of supplementary air, for instance, in quantities
corresponding to a theoretical air/fuel ratio, to ensure accurate
and stable control of the idling rpm of the engine.
FIGS. 6 shows flow charts for a routine for control of the first
control valve 6, executed within the ECU 9 in FIG. 1.
The present program is executed in sychronism with generation of
the TDC signal, and initiated after the ignition switch, not shown,
is turned on to initialize the ECU 9 (step 1 of (a) of FIG. 6).
When the TDC signal from the engine rpm sensor 14 in.FIG. 1 is
inputted to the ECU 9 (step 2), it is first determined whether or
not the engine rpm Ne is lower than cranking rpm NeCR (e.g. 400
rpm) and whether or not the engine starter switch is in an
on-state, at the step 3. If the answer to this question is yes,
that is, the engine is determined to be cranking, the duty factor
DOUT for the valve opening period of the first control valve 6 is
set to 100 percent so as to supply a maximum amount of
supplementary air to the engine 1, thereby obtaining stable
starting of the engine and allowing the engine rpm to reach the
idling rpm promptly (step 4). This duty factor setting is called
"full opening mode control". If the answer to the question of the
step 3 is no, the program proceeds to the steps 5 through 7. These
steps 5 through 7 are in accordance with the manner of control of
the first control valve 6 according to this invention, hereinafter
described in detail, wherein the duty factor DOUT for the valve
opening period of the first control valve 6 is continued to be set
to 100 percent for a period of time tIU which is determined by the
engine cooling water temperature, immediately after completion of
the engine cranking, that is, immediately after the engine rpm Ne
has risen above the cranking rpm NeCR or the engine starter switch
has been turned off from an on-state.
Upon determination of the lapse of the predetermined period of time
tIU from the completion of the engine cranking at the step 7, the
program proceeds to the step 8, where it is determined whether or
not a value Me proportional to the reciprocal of the engine rpm Ne
is larger than a value MA proportional to the reciprocal of a
predetermined value NA (e.g. 1,500 rpm) larger than desired idling
rpm. The above reciprocal values Me, MA are applied for the
convenience of processing within the ECU 9, and represent the time
interval between adjacent pulses of a pulse signal generated in
synchronism with the rotation of the engine. That is, the higher
the engine rpm, the smaller the time interval becomes.
If the answer to the question of the step 8 is no (Me<MA), that
is, the engine rpm Ne is higher than the predetermined rpm NA, the
ECU 9 sets the duty factor DOUT to zero at the step 9, so as to
interrupt the supply of any control signal for the first control
valve 6 to fully close same, because on such occasion the supply of
supplementary air to the engine 1 is not necessary as there is no
possibility of engine stall and fluctuations in the engine
rotation. This setting of the duty factor is hereinafter called
"supply stop mode control". Since the first control valve 6 is thus
deenergized when no supply of supplementary air is required, the
solenoid 6a will not overheat and repeated on-off actions of the
valve body 6b can be avoided to lengthen the effective life of the
valve 6.
If the answer to the question of the step 8 is yes, (Me.gtoreq.MA),
that is, when the engine rpm Ne is still lower than or equal to the
predetermined rpm NA, the program proceeds to the next step 10,
where it is determined whether or not the engine cooling water
temperature TW is higher than a predetermined value TWAIC0 (e.g.
50.degree. C.). If the result of determination of the step 10 gives
a negative answer, that is, when the engine cooling water
temperature TW is lower than or equal to the predetermined value
TWAIC0, the fast idling control device 34 in FIG. 1 is then already
operating as previously stated, and accordingly no supply of
supplementary air to the engine through the first control valve 6
is necessary in addition to the supply of the same air through the
fast idling control device 34. Therefore, the duty factor DOUT for
the valve opening period of the first control valve 6 is set to
zero, at the step 9, rendering the first control valve 6
inoperative.
If the result of the determination of the step 10 gives an
affirmative answer, it is then determined at the next step 11
whether or not the valve opening .theta.th of the throttle valve 5
in FIG. 1 is smaller than a predetermined value .theta.IDL which is
so small as can be substantially regarded as zero. If the answer to
the question of the step 11 is yes, the program proceeds to the
step 12 ((b) of FIG. 6), where values MH and ML are determined,
which correspond, respectively, to the reciprocal of an upper limit
NH of a desired idling rpm range and the reciprocal of a lower
limit NL of same, in a manner hereinafter described in detail.
Following this, a determination is made as to whether or not the
value Me corresponding to the reciprocal of engine rpm Ne is larger
than the value MH, at the step 13. If the result of this
determination gives a negative answer (Me<MH), that is, when the
engine rpm Ne is larger than the upper limit NH of the desired
idling rpm range, it is then determined whether or not the
preceding loop of the program was in feedback mode, at the step 14.
If the answer is no, it is regarded that the engine is operating in
decelerating mode, and the program proceeds to the steps 15 through
17 wherein the valve opening duty factor for the first control
valve 6 is calculated, as hereinafter referred to. More
specifically, at the step 15, a term DX of the duty factor DOUT
(hereinafter called "decelerating mode term") is calculated so as
to gradually increase with a reduction in the engine rpm, while at
the step 16, another term DE of the duty factor DOUT (hereinafter
called "electrical load term") is determined in dependence on the
electrical load on the engine. Thereafter, at the step 17, the sum
of the two terms DX and DE is calculated to obtain the value of the
valve opening duty factor DOUT. At the step 16, a further
determination is made of the value of a constant TAIC to be added
to or subtracted from the valve opening period of the fuel
injection valve predetermined times of injection after there occurs
a change in the electrical load on the engine, as also hereinafter
described in detail.
If the answer to the step 13 becomes affirmative (Me.gtoreq.MH),
that is, when the engine rpm Ne becomes smaller than or equal to
the upper limit NH of the desired idling rpm range, the program
proceeds to feedback mode control at engine idle, as hereinafter
referred to, wherein the value of the constant TAIC is determined
at the step 18, and further, calculation of the duty factor DOUT is
carried out by adding the aforementioned electrical load term DE to
a feedback mode control term DPIN, at the step 19. Even if the
result of the determination of the step 14 gives an affirmative
answer, the program proceeds to the steps 18 and 19 to carry out
the feedback mode control of the valve opening period of the first
control valve 6. This means that even in the event of the engine
rpm jumping over the upper limit NH of the desired idling rpm
range, the feedback mode control is continued so far as the
preceding loop was in the same feedback mode and the throttle valve
5 remains fully closed.
When the throttle valve 5 is opened from its fully closed state
during the feedback mode control, the result of the determination
of the step 11 in (a) of FIG. 6 will give a negative answer or no,
that is, as hereinafter described in detail, it is regarded that
the engine has entered the accelerating mode region, and following
a determination at the step 20, hereinafter referred to,
determinations are made of the values of the electrical load term
DE and the constant TAIC at the step 21, and then at the step 22,
the value of the valve opening duty factor DOUT is determined which
correponds to the sum of the determined values DE, TAIC and also an
acceleration mode term which gradually decreases in value with an
increase in the engine rpm during accelerating mode control.
At the step 20, it is determined whether or not the valve opening
duty factor DOUT is smaller than a fine value Do with which the
valve body 6b of the first control valve 6 will not substantially
open even if the solenoid 6a of the same valve is energized
(hereinafter called "ineffective duty factor value"). During
accelerating mode control, with an increase in the engine rpm, the
duty factor DOUT is reduced and finally even to the ineffective
duty factor value Do, to establish the relationship of
DOUT.ltoreq.Do at the step 20. After this, the duty factor DOUT is
set to zero, at the step 9 of (a) of FIG. 6, deenergizing the
solenoid 6a of the first control valve 6 to render the valve
inoperative.
After completion of the calculations of the duty factor DOUT for
the valve opening period of the first control valve 6 in accordance
with various operating conditions of the engine, the program
proceeds to the step 23 in (a) of FIG. 6, wherein calculations are
made of the valve opening period TOUT for the first control valve
6, the valve opening delaying period of time TDLY, already referred
to with reference to FIG. 5, and the valve opening period TIOUT for
the fuel injection valve 10, followed by termination of execution
of the present program at the step 24.
FIGS. 7 through 9 show manners of controlling the valve opening
period for the first control valve 6, respectively, in decelerating
mode, feedback mode, and accelerating mode, already explained with
reference to FIG. 6.
Control of First Control Valve in Decelerating Mode
As shown in FIG. 7, when the throttle valve 5 is fully closed to
decelerate the engine so that the engine speed decreases with the
lapse of time and below the aforementioned predetermined value NA
(e.g. 1,500 rpm) ((a) of FIG. 7), the first control valve 6 is
opened to allow supply of the supplementary air to the engine 1
through the first air passage 8 to initiate control of the
supplementary air quantity in decelerating mode.
In this decelerating mode, the supplementary air quantity or the
valve opening duty factor of the first control valve 6 is set so as
to increase with a decrease in the engine rpm, and it is controlled
to a predetermined duty factor DXH when the engine speed Ne
decreases to the upper limit NH of the desired idling rpm range, as
shown in FIG. 7. FIG. 8 shows an example of the relationship
between the duty factor DX for the first control valve 6 and the
engine rpm, applicable during the decelerating mode control. As
shown in the graph, when the engine rpm Ne lies between the
predetermined rpm NA and the upper limit NH of the desired idling
rpm range, the duty factor DX is set to a value variable with a
change in the value Me proportional to the reciprocal of the engine
rpm Ne. When the value of engine rpm Ne is larger than or equal to
the predetermined value NA (Me.ltoreq.MA), the value DX is set to
zero, while when the value of engine rpm is smaller than or equal
to the value NH (Me.gtoreq.MH), the value DX is set to the
predetermined fixed value DXH.
In the above described manner, by gradually increasing the quantity
of supplementary air with a decrease in the engine rpm from the
predetermined value NA during engine deceleration with the throttle
valve fully closed, the phenomenon can be prevented that the engine
speed suddenly drops upon disengagement of the engine clutch during
the engine deceleration, causing engine stall.
As previously explained with reference to the steps 15 through 17
of (b) of FIG. 6, during the decelerating mode control the duty
factor for the valve opening period of the first control valve 6 is
given by the sum of the decelerating mode term DX and the
electrical load term DE. Although the foregoing description
referring to FIG. 7 is based upon the omission of the electrical
load term DE, a similar control manner in which the same term is
applied as well, will be hereinafter described.
Control of First Control Valve in Feedback Mode
When the engine speed further decreases below the upper limit NH of
the desired idling rpm range, the supplementary air quantity is now
controlled in feedback mode so as to maintain the engine rpm Ne
between the upper limit NH and the lower NL of the desired idling
rpm range. These upper and lower limits of the desired idling rpm
range are provided for stable control of the idling rpm. They are
set at values higher and lower by a predetermined rpm value (e.g.
30 rpm) than a central value of the desired idling rpm range which
is set to a value appropriate to the engine operation in dependence
upon engine cooling water temperature, electrical loads of the
electrical devices 18, 19, 20, etc. or mechanical loads of the
mechanical load creating devices in the engine such as the air
conditioner, each time there occurs a change in any of these
parameters. When the actual engine speed lies between the upper
limit NH and the lower limit NL, the ECU 9 regards that the engine
rpm is equal to the desired idling rpm.
The idling rpm feedback control in feedback mode is carried out as
follows: The ECU 9 detects the difference between the upper or
lower limit NH or NL of the desired idling rpm range set to a value
depending upon engine load as previously mentioned, and the actual
engine rpm Ne obtained by the engine rpm sensor 14, sets the duty
factor for the valve opening period of the first control valve 6 to
such a value as corresponds to the detected difference and makes
the same difference zero, and opens the control valve 6 for a
period of time corresponding to the set duty factor to control the
supplementary air quantity, thereby controlling the engine rpm to a
value between the upper and lower limits NH and NL, i.e. the
desired engine rpm.
During the above feedback control of the supplementary air quantity
at engine idle, the engine speed can temporarily rise above the
upper desired rpm limit NH, due to external disturbances or
extinction of the engine load caused by switching-off of the
electric devices 15, as indicated by the symbol Sn in FIG. 7. In
such event, the ECU 9 determines whether or not control of the
supplementary air quantity in the preceding loop was effected in
feedback mode. This determination is provided to ensure
continuation of the idling rpm feedback control without being
affected by disturbances in the engine rpm caused by external
disturbances etc. once the same feedback control has been
initiated. In the example of FIG. 6, it is noted that the preceding
loop Sn-1 was in feedback mode. Therefore, the feedback control is
continued also in the present loop Sn. Further, in the FIG. 6
example, it will be also determined by the ECU 9 that the present
loop Sn is in feedback mode if the engine speed still exceeds the
upper limit NH in the next loop Sn+1 as in the same example, and
the feedback control will be continued also in the next loop. In
this manner, once the feedback control has been started immediately
after termination of the decelerating mode control, the same
feedback control is continuously effected so long as the throttle
valve 5 is kept closed, even if the engine speed temporarily rises
above the upper limit NH due to external disturbances, to thereby
achieve stable idling rpm feedback control.
On the other hand, during the control in decelerating mode, so long
as the engine speed remains above the upper limit NH as indicated
by the symbol Sk in FIG. 6, the ECU 9 determines whether or not the
preceding loop Sk-1 was in decelerating mode, and continues the
decelerating mode control also in the present loop Sk if the
preceding loop was in decelerating mode. This makes it possible to
avoid that the ECU 9 wrongly judges that the engine is in a
feedback-mode controlling region, though in fact the engine is
still in a decelerating-mode controlling region with the engine rpm
above the upper idling rpm limit NH, and also that the valve
opening period of the first control valve 6 is controlled to an
extremely small value when the feedback control is erroneously
carried out due to the above misjudgement, causing engine stall
upon disengagement of the clutch.
Also when the engine rpm Ne drops below the lower limit NL, the
difference between the same lower limit NL and the actual engine
rpm Ne is determined, on the basis of which is determined the duty
factor for the valve opening period of the first control valve 6 so
as to increase the actual engine rpm Ne with an increase in the
above difference.
The manner of setting the duty factor for the valve opening period
of the first control valve 6 in feedback mode will be hereinafter
described in detail.
Control of First Control Valve in Accelerating Mode
When the throttle valve 5 is opened for starting the vehicle during
the feedback control of the idling engine rpm, the engine rpm Ne
increases as shown in (a) of FIG. 9. Even with the throttle valve 5
thus opened, the supplementary air quantity is not suddenly reduced
to zero, but the supplementary air is continuously supplied to the
engine in a quantity equal to that applied during the feedback mode
control immediately preceding the opening of the throttle valve 5,
and thereafter the same supplementary air quantity is reduced by a
predetermined amount, for instance, each time each pulse of the TDC
signal is inputted to the ECU 9, as shown as accelerating mode in
(b) of FIG. 9. This manner of controlling the supplementary air
quantity can prevent a sudden drop in the engine speed and permit
smooth engagement of the clutch without occurrence of engine
stall.
During the accelerating mode control, the duty factor DOUT for the
valve opening period of the first control valve 6 gradually
decreases with an increase in the engine speed, and even reaches
the fine ineffective duty factor value Do at which the valve body
6b of the first control valve 6 will not assume a substantially
opened position even with the solenoid 6a energized. Once this
ineffective duty factor value Do is reached, the duty factor DOUT
is set to zero, as supply stop mode in (b) of FIG. 9, whereby the
solenoid 6a of the first control valve 6 is deenergized to render
the same valve inoperative, thereby improving the effective life of
the valve body 6b and preventing overheating of the solenoid 6a and
any other adverse influence derived therefrom.
Setting of Upper and Lower Limits of Desired Idling RPM Range
Reference is now made to the manners of setting the values of MH
and ML corresponding to the reciprocals of the upper and lower
limits NH and NL of the desired idling rpm range, which are
determined at the step 12 in (b) of FIG. 6.
The value of engine rpm that is desired at engine idle is
determined in dependence on an engine temperature-indicative signal
from the engine cooling water temperature sensor 13, signals
indicative of various electrical loads from the switches 21, 22 and
23 of the electrical devices 18, 19 and 20 such as head lamps, and
an on-off state signal from the air conditioner, and a D-range
signal from the automatic transmission, all the signals being
supplied to the ECU 9 in FIG. 1. However, in the following
explanation, it is assumed for the convenience of explanation that
the desired value of idling rpm is set in dependence on the engine
cooling water temperature signal, the on-off state signal from the
air conditioner and the D-range signal from the automatic
transmission, alone.
FIG. 10 shows a flow chart of a routine for setting the desired
idling rpm value, executed within the ECU 9 in FIG. 1. This routine
is comprised of a block I for setting the desired idling rpm value
in dependence on the engine cooling water temperature, a block II
for setting the desired idling rpm value in dependence on the
on-off state of the air conditioner, a block III for setting the
same value in dependence on the on-off state of the automatic
transmission, and a block IV for selecting a maximum one of the
desired idling rpm values set in the blocks I, II and III.
When the program is called within the ECU 9, at the step 1 in FIG.
10, first a value MTW is determined which is proportional to the
reciprocal of the desired idling rpm value and determined by the
engine cooling water temperature, at the step 2 The value MTW is
set to larger values (smaller values in terms of engine rpm Ne) as
the engine cooling water temperature increases, as shown in FIG.
11, for instance. A plurality of predetermined values of the value
MTW are previously stored in a map within the ECU 9, as functions
of the engine cooling water temperature TW.
Next, a determination is made as to whether or not the switch 15 of
the air conditioner is in an on-state, at the step 3. If the result
of the determination gives a negative answer, that is, if the air
conditioner is inoperative, a provisional value MAC is selected as
a value equivalent to a value MTW read at the step 2, at the step
4, and the program proceeds to the step 6. If the result of the
determination of the step 3 gives an affirmative answer, that is,
if the air conditioner is operative, the provisional value MAC is
set to a value MAC0 which is proportional to the reciprocal of
engine rpm which is higher by a predetermined increment
corresponding to the load of the air conditioner, than normal
idling rpm at a standard value (e.g. 70.degree. C.) of the engine
cooling water temperature. The above value MAC0 is experimentally
determined in advance.
Then, at the step 6, a determination is made as to whether or not
the D-range signal of the automatic transmission is being inputted
to the ECU 9, that is, whether or not the automatic transmission is
in an engaged state. If the answer to this question is negative, a
provisional value MAT is selected as a value equivalent to a value
MTW read at the step 2, at the step 7, and the program proceeds to
the step 8. If the answer to the question of the step 6 is
affirmative, that is, when the automatic transmission is engaged
and its load is acting upon the engine 1, the provisional value MAT
is set to a value MAT0, at the step 9, which is proportional to the
reciprocal of engine rpm which is higher by a predetermined
increment corresponding to the load of the automatic transmission,
than the above normal idling rpm at the standard engine cooling
water temperature, the value MAT0 being also previously
experimentally determined, followed by the program proceeding to
the step 8.
At the step 8, it is determined whether or not the value MTW
determined as above is smaller than or equal to the provisional
value MAT, and if the answer is no, that is, if the value MTW is
larger than the provisional value MAT, a further provisional value
MX is set to a value equal to the provisional value MAT, at the
step 9, while if the answer is yes, the same value MX is set to a
value equal to the value MTW, at the step 10. It will be noted that
at the steps 8 through 10, the smaller one of the values MTW and
MAT, that is, the larger one of the desired idling rpm values is
selected.
In a manner similar to the above, at the step 11, a comparison is
made between the provisional value MX and the provisional value
MAC, and the smaller one of which is set to a value MFB, at the
steps 12 and 13, then terminating execution of the program. That
is, in these steps 8 through 13, the smallest one of the values
MTW, MAT and MAC, that is, the largest one of the corresponding
desired idling rpm values is selected as the value MFB.
Upper and lower limit values MH and ML of the value MFB thus
selected are then determined at the step 12 of (b) of FIG. 6. Such
upper and lower limits MH, ML are provided for stable control of
the idling rpm. The values of the upper and lower limits NH, NL are
set to values, respectively, higher and lower than the desired
idling rpm value NFB, by predetermined rpm (e.g. 30 rpm) which is
dependent upon the operating characteristics of the engine
concerned, and then corresponding values MH and ML are determined
from the values NH, NL thus set.
Although in the example of FIG. 10, the three loads to be applied
on the engine, such as that of the air conditioner, are used, a
similar manner of setting of the desired idling rpm can apply to an
example in which further loads are involved, besides the above
three loads.
Next, detailed explanations will now be given about control of the
supplementary air quantity upon a change in the electrical load on
the engine during engine rpm control in feedback mode, decelerating
mode and accelerating mode, calculations of the duty factor for the
valve opening period of the first control valve in such various
modes, and control of the fuel quantity immediately after a change
in the engine load such as electrical load, by referring to FIGS.
12 through 17.
Control of Idling RPM in the Event of Addition of an Electrical
Load on the Engine Load during Feedback Mode Control
FIG. 12 shows a manner of increasing the supplementary air quantity
in the event of an electrical load being added to the engine load
during feedback mode control of the idling rpm. As shown in (a) of
FIG. 12, during engine idle, the engine rpm Ne is controlled in
feedback mode so as to be maintained between the upper and lower
limits NH, NL of the desired idling rpm range. Let it now be
assumed that during this feedback mode control at least one of the
switches 21, 22, and 23 of the first, second, and third electrical
devices 18, 19 and 20 is closed to apply at least one electrical
load on the engine 1, all appearing in FIG. 1, as shown in (b) of
FIG. 12. If no countermeasure is taken in such event, the engine
rpm Ne will largely drop as indicated by the broken line in (a) of
FIG. 12, by an amount corresponding to the magnitude of the added
electrical load. Responsive to such drop in the engine rpm Ne, the
supply quantity of supplementary air is increased as indicated by
the broken line in (c) of FIG. 12, so that with the lapse of time
the engine rpm Ne will gradually recover into the desired idling
rpm range between the upper and lower limits NH, NL.
Various incremental amounts of supplementary air required for
maintaining the engine rpm Ne at the desired idling rpm upon
application of an electrical load on the engine (shown as an
increment DE of the duty factor for the first control valve 6 in
(c) of FIG. 12) can be estimated in advance, depending upon the
kinds of the electrical devices which produce such electrical
loads. Therefore, various values of the electrical load term DE are
determined in advance for respective ones of the electrical
devices, and when the on-state signal of one of the electrical
devices is inputted to the ECU 9, a corresponding one of the above
predetermined electrical load term values DE is selected, at the
step 18 in (b) of FIG. 6, and this selected electrical term value
DE is added to the feedback mode term DPIN to determine the duty
factor DOUT for the first control valve 6, as shown in (c) of FIG.
12.
By increasing the supplementary air quantity upon application of a
new electrical load on the engine in the above way, the engine rpm
can be promptly recovered to the desired idling rpm, with a greatly
reduced response lag in the feedback control ((a) and (c) of FIG.
12).
The duty factor DOUT for the valve opening period of the first
control valve 6 applicable during feedback mode control is
calculated by the following equation, which is executed at the step
19 in (b) of FIG. 6:
where the electrical load term DE is determined at the step 18 in
FIG. 6.
FIG. 13 shows a flow chart of a subroutine for calculation of the
value DE, executed in the step 18 in (b) of FIG. 6. When this
program is called at the step 1 in FIG. 13, the stored value of DE
is reset to zero at the step 2. Next, at the step 3, it is
determined whether or not the switch 21 of the first electrical
device 18, shown in FIG. 1, is in on-state. If the answer to this
question is no, the program proceeds to the step 5. If, at the step
3, the answer is yes, a predetermined electrical load term DE.sub.1
corresponding to the electrical load produced by the first
electrical device 18 is added to the stored value of the electrical
load term DE and the resulting sum value DE+DE.sub.1 is set as a
new stored value of electrical load term DE for the first
electrical device 18 in the step 4. Since, in this case, the stored
value of DE is reset to zero (DE=0) at the step 2, the newly stored
value of the electrical load term DE+DE.sub.1 is equal to
DE.sub.1.
Then, in the aforesaid manner, the on-off state of the switch 22 of
the second electrical device 19 is determined in the step 5. If it
is not in on-state, the program proceeds to the step 7 and if it is
in on-state, a predetermined electrical load term DE.sub.2 relating
to the electrical load produced by the second electrical device 19
is added to the stored value of electrical load term DE, and the
resulting sum value DE+DE.sub.2 is set as a new stored value of
electrical load term DE for the electrical device 19, at the step
6. Further, in the aforesaid manner, the on-off state of the switch
21 of the third electric device 20 is determined at the step 7. If
it is not in on-state, the program is terminated at the step 9, and
if it is in on-state, a predetermined electrical load term DE.sub.3
relating to the third electrical device 20 is added to the stored
value of the electrical load term DE and the resulting sum value
DE+DE.sub.3 is set as a new stored value of electrical load term DE
for the electrical device 20 in the step 8, and then execution of
the program is terminated.
In the manner explained hereabove, the electrical load term DE in
the equation (1) is determined by first determining the respective
on-off states of the first, second and third electrical devices 18,
19 and 20 and for each electrical device that is in on-state, a
predetermined electrical load term relating to the electrical load
produced by the device is added to the stored value of the
electrical load term DE, and this new value is set as the updated
electrical load term DE.
The value of the feedback mode term DPIN in the above equation (1)
is determined, e.g. by a subroutine shown in FIG. 3. The program
concerned is called at the step 1 in FIG. 14, and then it is
determined whether or not the value Me which is proportional to the
reciprocal of the actual engine rpm is smaller than the value MH
that corresponds to the upper limit NH of the desired idling rpm
range determined at the step 12 in (b) of FIG. 6, at the step 2. If
the answer to the question of the step 2 is negative, that is,
Ne.ltoreq.NH, the program proceeds to the step 3, where it is
determined whether or not the value of Me is larger than the value
of ML, which corresponds to the reciprocal of the lower limit NL of
the desired idling rpm range. If the answer to the question of the
step 3 is negative, that is, if as a result of the determinations
of the steps 2 and 3, the actual engine rpm is found to be between
the upper and lower limits NH and NL of the desired idling rpm
range, the difference .DELTA.Mn between the value Me and the values
MH, ML is set to zero at the step 4, since it is then not necessary
to either increase or decrease the actual engine rpm Ne. Then, the
value of the feedback mode term DPIN is set to a value DPIN-1
obtained in the preceding loop, at the step 5, followed by
terminating the execution of the present loop, at the step 6.
If the determination of the step 3 gives an affirmative answer or
yes, it is regarded the actual engine rpm Ne is smaller than the
lower limit NL, and then the value of the difference .DELTA.Mn
(which then assumes a positive value or plus sign) is calculated,
at the step 7. This value .DELTA.Mn is then multiplied by a
constant KI to obtain an integral control term value .DELTA.DI, at
the step 8. Then, the difference between the difference value
.DELTA.Mn calculated at the step 7 and the same value .DELTA.Mn-1
obtained in the previous loop, that is, the acceleration
differential value .DELTA..DELTA.Mn, is calculated at the step 9.
This acceleration differential value .DELTA..DELTA.Mn is multiplied
by a constant Kp to obtain a proportional control term value
.DELTA.DP at the step 10. The integral control term value .DELTA.DI
and the proportional control term value .DELTA.DP, are added to the
aforementioned feedback control term value DPIN-1 to obtain a
feedback control term value DPIN as an up-to-date value, at the
step 11. Then, the execution of the program is terminated at the
step 6.
If the answer to the question of the step 2 is affirmative or yes,
it is determined that the actual engine rpm Ne is larger than the
upper limit NH of the desired idling rpm range, and at the step 12,
the above differential value .DELTA.Mn is calculated which then
assumes a negative value or minus sign. Thence, the integral
control term value .DELTA.DI, the proportional control term value
.DELTA.DP, and the present loop feedback control term value DPIN
are calculated, respectively, at the steps 8, 10 and 11, followed
by termination of the execution of the program.
Control of Engine RPM in the Event of Addition of an Electrical
Load on the Engine Load during Decelerating Mode Control
FIG. 15 shows a manner of control of the supplementary air
quantity, applied in the event that an electrical load is applied
on the engine during the decelerating mode control as explained
previously with reference to FIG. 7.
When the engine rpm decreases with the throttle valve 5 in FIG. 1
fully closed, and falls below the predetermined value of engine rpm
NA, the first control valve 6 opens to start the supply of
supplementary air to the engine in the decelerating mode control as
shown in (a) and (c) of FIG. 15.
When an electrical load is added to the engine load while the
engine is in the deceleration mode control, as shown in (b) of FIG.
15, the engine load increases in the same way as during feedback
mode control as shown in FIG. 12. On such occasion, despite the
supply of gradually increased quantity of supplementary air to the
engine in decelerating mode control the quantity of such increased
amount of supplementary air can be insufficient causing the engine
rpm to abruptly drop as shown by the broken line in (a) of FIG. 15
and depending on the magnitude of the electrical load, can result
in engine stall, particularly when the clutch is already in a state
of disengagement.
Even when the engine is in decelerating mode control, it is
possible to estimate the necessary quantity of supplementary air to
be supplied to the engine in proportion to the electrical load that
corresponds to the kind of the electrical device, that is in
on-state. Therefore, according to the invention, the signal
indicative of the on-off state of the electrical devices is
monitored, and simultaneously when the signal turns on, the duty
factor DOUT of the first control valve 6 is increased by an amount
corresponding to the electrical load term DE relating to the
electrical device that is switched on, determined as previously
explained with reference to FIG. 13 ((c) of FIG. 15 and steps 16
and 17 in (b) of FIG. 6). That is, the duty factor DOUT is
determined by the following equation:
where DX is a deceleration mode term which is determined as a
function of engine rpm.
In the aforesaid manner, by supplying an increased amount of
supplementary air, as calculated by the use of the equation (2), to
the engine at the same time as an electrical load is added to the
engine load, not only can an abrupt drop in the engine rpm be
avoided but the driveability of the engine can also be
improved.
Control of Engine RPM in the Event of Addition of Electrical Load
on Engine Load during Accelerating Mode Control
Next, FIG. 16 shows a method for controlling the increase in the
quantity of supplementary air to be supplied to the engine,
applicable in the event that an electrical load is applied on the
engine while the engine is accelerating with the throttle valve 5,
shown in FIG. 1, opened from a state of idle in feedback mode
control. When the engine is accelerated with the throttle valve 5
fully opened from a state of idle with the throttle valve 5 fully
closed in feedback mode control as shown in (a) of FIG. 16, the
control of supply of supplementary air is effected in accelerating
mode as previously explained with reference to FIG. 9 ((b) of FIG.
16).
If an electrical load is applied on the engine, during the above
acceleration mode control of the engine 1((b) in FIG. 16), this
electrical load increases the engine load and accordingly the
engine rpm Ne abruptly decreases (the broken line in (a) of FIG.
16), causing discomfort to the driver and badly affecting the
driveability of the engine, as in the feedback mode control and in
the deceleration mode control previously explained with reference
to FIG. 12 and FIG. 15, respectively. Even during the acceleration
mode control, in the same manner as explained with reference to
FIG. 12, it is possible to estimate the necessary quantity of
supplementary air supplied to the engine corresponding to each kind
of electrical device that produces the electrical load. Therefore,
also during this acceleration mode control, the on-state signal of
each electrical device indicative of the occurrence of electrical
load is monitored, and simultaneously with the output of on-state
signal the duty factor DOUT for the control valve 6 is increased
just by the electrical load term DE as shown in (c) in FIG. 16.
That is, the duty factor DOUT is determined by the following
equation:
where DPI.sub.n-1 is a duty factor determined in the last control
loop in feedback mode control immediately before the opening of the
throttle valve and determined in the manner shown in FIG. 14, DA is
a constant determined experimentally, and m indicates the number of
pulses of the TDC signal counted from the time the throttle valve 5
is opened. The electrical load term DE is determined in the same
manner as previously explained with reference to FIG. 13.
An increased quantity of supplementary air, as calculated by the
above equation (3), is supplied to the engine simultaneously with
the occurrence of an electrical load on the engine, not only
preventing any abrupt drop in the engine rpm but also improving the
driveability of the engine.
Manner of Control of Fuel Quantity after a Change in the Engine
Load
Details of the manner for controlling the supply of fuel through
the fuel injection valve 10 after a change in the engine load
including both electrical and mechanical loads during engine rpm
control will now be described with reference to FIG. 17. This fuel
supply control method corresponds to the manner of setting the
value TAIC in the steps 16, 18 and 21 in (b) and (c) of FIG. 6.
FIG. 17, shows a timing chart of the manner of varying the fuel
quantity to be supplied to the engine 1 when there is a change in
the operative states of the electrical devices, etc. during control
of the idling rpm. For the convenience of explanation, each TDC
pulse is numbered in the sequence of generation as a TDC pulse 1,
2, 3 . . . and a first explanation given below is based upon the
assumption that during the time between generation of the first TDC
pulse 1 and generation of the nineteenth TDC pulse 19, the first
electrical device 18 alone is switched on and off, and a second
explanation on the assumption that during the time between the
generations of the above two pulses, also the air conditioner is
switched on and off in addition to the first electrical device 18,
respectively.
Let it now be assumed that the first electrical device 18 is
switched on at a time between a TDC pulse 2 and a TDC pulse 3 and
switched off at a time between a TDC pulse 8 and a TDC pulse 9 ((b)
of FIG. 17). The ECU 9 detects a signal indicative of the on-state
of the first electrical device 18 immediately after the generation
of the TDC pulse 3 and accordingly calculates a value of the duty
factor DOUT of the first control valve 6 corresponding to a
quantity of supplementary air which is increased by a predetermined
amount dependent upon the magnitude of the electrical load on the
engine, applied by the first electrical device 18. The first
control valve 6 is opened for a valve opening period corresponding
to the calculated duty factor DOUT. Similarly, even after
generation of a TDC pulse 4, the ECU 9 continuously calculates the
above same value of the duty factor DOUT corresponding to the
increased supplementary air quantity dependent upon the load of the
first electrical device 18, and continuously causes opening of the
first control valve 6 for a valve opening period corresponding to
the calculated duty factor DOUT until it is supplied with a signal
indicative of the off-state of the same device. The increased
supplementary air, which is determined and supplied immediately
after the generation of the TDC pulse 3 as noted above, actually
does not reach a cylinder of the engine 1 until after generation of
a TDC pulse 5, as shown in (a) of FIG. 17. This suction delay time
is determined by the passage configuration and size of the intake
system of the engine, etc. and can be determined theoretically or
experimentally. Further, the engine 1 is not supplied with a
quantity of fuel which exactly corresponds to the above increased
supplementary air until after generation of a TDC pulse 8. This is
because the gradual increase of the intake air quantity during the
time between the generation of the TDC pulse 5 and the generation
of the TDC pulse 8 cannot be accurately detected mainly owing to
the detection lag of the absolute pressure sensor 12 ((a) of FIG.
17). Therefore, while the increased air quantity is supplied to the
engine 1 from a time immediately after generation of the TDC pulse
5 to a time immediately after generation of the TDC pulse 7, the
increase of the fuel supply quantity cannot promptly follow the
increase of the intake air quantity, resulting in a shortage in the
fuel quantity. Consequently, the mixture supplied to the engine 1
becomes too lean, which can even cause engine stall, hunting of the
engine rotation, etc.
Then, an off-state signal indicative of the switching-off of the
first electrical device 18 that is switched off at a time between
generations of the TDC pulses 8 and 9, is detected immediately
after generation of the TDC pulse 9. Since the switching-off of the
first electrical device 18 means a reduction in the engine load, a
value of the supplementary air quantity is calculated at a time
immediately after generation of the TDC pulse 9, which is decreased
from the preceding value by a predetermined amount corresponding to
the electrical load of the first electrical device 18, and supplied
to the engine 1 through the first control valve 6. Also in this
event, the decreased supplementary air quantity is not actually
supplied to the engine cylinder until after generation of a TDC
pulse 11, due to the travel lag attributed to the passage
configuration and size of the intake system, etc. Although the
intake air quantity gradually decreases during the time between the
generation of the a pulse 11 and the generation of the TDC pulse
14, the decreased fuel supply to the engine 1 cannot promptly
follow the decrease of the intake air quantity due to the detection
lag of the absolute pressure sensor 12, etc., causing supply of an
excessive quantity of fuel to the engine and consequent excessive
enrichment of the mixture, deteriorating the emission
characteristics, and occurrence of hunting of the engine rotation,
etc. during idling ((a) and (b) of FIG. 17).
The above-mentioned disadvantages can be eliminated in the
following manner: After the supplementary air quantity supplied
through the first control valve 6 has been increased immediately
after the generation of the TDC pulse 3, and after the lapse of a
period between the generation of the TDC pulse 3 and a time
immediately before the generation of the TDC pulse 5 (hereinafter
called "the fuel increase-delaying period"), the quantity of fuel
supplied to the engine 1 is increased by a predetermined amount
during the period between a time immediately after the generation
of the TDC pulse 5 and a time immediately after the generation of
the TDC pulse 7 (this period will be hereinafter called "the fuel
increasing period"). On the other hand, after the supplementary air
quantity has been decreased immediately after the generation of the
TDC pulse 9, and after the lapse of a period between the generation
of the TDC pulse 9 and a time immediately before the generation of
the TDC pulse 11 (hereinafter called "the fuel decrease-delaying
period"), the fuel supply quantity is decreased by a predetermined
amount during the period between a time immediately after the
generation of the TDC pulse 11 and a time immediately after the
generation of the TDC pulse 13 (hereinafter called "fuel decreasing
period").
The above manner of increase and decrease of fuel according to the
invention will now be described in further detail: Upon detection
of an on-state signal from the first electrical device 18, a
counter CP1 in the ECU 9 in FIG. 1 has its count set to a
predetermined value, 2 for instance, which is determined by the
passage configuration and size of the intake system, and other
factors, and thenceafter the above newly set count is reduced by 1
upon inputting of each TDC pulse to the ECU 9 ((b) and (c) of FIG.
17). That is, the count in the counter CP1 occurring immediately
after the generation of the TDC pulse 4 is set to 1, and the one
occurring immediately after the generation of the TDC pulse 5 to 0,
respectively. The time during which the count in the counter CP1 is
other than 0 corresponds to the aforementioned fuel
increase-delaying period, and when the count in the counter CP1
becomes zero, the above fuel increasing period starts. When the
count in the counter CP1 becomes zero immediately after the
generation of the TDC pulse 5, the count in another counter NP1 in
the ECU 9 is set to a predetermined value, 3 for instance, which
depends upon the magnitude of the load of the first electrical
device 18 on the engine and corresponds to the aforementioned fuel
increasing period. At the same time, the valve opening period TOUT
of the fuel injection valve 10 is set to a value increased by a
predetermined period TAICP corresponding to the detection error of
the intake air quantity mainly attributed to the detection lag of
the absolute pressure sensor 12. That is, the valve opening period
TIOUT of the fuel injection valve 10 is calculated by the following
equation:
where Ti represents a value calculated on the basis of values of
engine operation parameter signals from the throttle valve opening
sensor 17, the absolute pressure sensor 12, the engine cooling
water temperature sensor 13, the engine rpm sensor 14, etc. and
TAIC is the aforementioned constant which is set to TAICP during
the above fuel increasing period.
The count in the counter NP1 is reduced by 1 upon inputting of each
TDC pulse to the ECU 9, and as long as the count NP1 is other than
0, that is, during the period between the generations of the TDC
pulses 5 and 7, the above predetermined value TAICP is added to the
value Ti of the valve opening period TIOUT of the fuel injection
valve 10 upon generation of each of these TDC pulses, and a
quantity of fuel corresponding to the calculated valve opening
period TIOUT is supplied to the engine 1 ((c) and (d) of FIG. 17).
The count in the counter NP1 becomes zero immediately after the
generation of the TDC pulse 8 ((c) of FIG. 17), and thereafter the
predetermined value TAICP is no longer added to the value Ti of the
valve opening period TIOUT (The value TAIC in equation (4) is set
to zero). Since by this time the delay time in detecting the
changing intake air, i.e. the fuel increasing period has already
lapsed, the intake air quantity can then be detected with accuracy
((a), (c) and (d) of FIG. 17), allowing the supply of fuel exactly
corresponding to the supplementary air quantity.
Next, when the off-state signal from the first electrical device 18
is detected at a time immediately after generation of the TDC pulse
9, the valve opening period of the first control valve 6 is reduced
by a predetermined amount dependent upon the magnitude of the load
of the first electrical device 18, and the count in another counter
CM1 in the ECU 9 is set to a predetermined value 2 (CM1=2) which
corresponds to the aforementioned fuel decrease-delaying period
((b) and (c) of FIG. 17). Then, this count of 2 is reduced by 1
each time each of the following TDC pulses is inputted to the ECU
9. As long as the count in the counter CM1 is other than 0, the
above fuel decrease-delaying period still continues, during which
neither increase or decrease of the fuel quantity is made by
setting and holding the value TAICP at 0 in (4) ((c) and (d) of
FIG. 17).
When the count in the counter CM1 becomes zero at a time
immediately after the generation of the TDC pulse 11, the count in
a counter NM1 in the ECU 9 is set to a predetermined value
dependent upon the magnitude of the first electrical device 18 on
the engine, 3 for instance which corresponds to the aforementioned
fuel decreasing period, and the valve opening period TIOUT of the
fuel injection valve 10 is decreased by a predetermined value
TAICM, that is, the valve opening period TIOUT is calculated by the
use of the equation (4) where the term TAIC is set to -TAICM. The
fuel supply is effected on the basis of the resulting calculated
value TIOUT. The count in the counter NM1 is reduced by 1 upon
inputting of each TDC pulse to the ECU 9, and the period during
which the count in the counter NM1 is other than 0 means the above
fuel decreasing period. During this period which lasts from a time
immediately after the generation of the TDC pulse 11 to a time
immediately after the generation of the TDC signal 13, the valve
opening period TIOUT is decreased by the predetermined value TAICM
to supply a decreased quantity of fuel to the engine ((a), (c) and
(d) of FIG. 17).
At a time immediately after generation of the TDC pulse 14, the
count in the counter NM1 becomes zero, and thereafter the
predetermined value TAICM is no more added to the basic value Ti
the valve opening period TIOUT (the value TAIC in the equation (4)
is set to zero). Since by this time the intake air detection delay
time or the fuel decreasing period has already lapsed so that
accurate detection of the intake air quantity is possible, to
enable supply of an accurate quantity of fuel to the engine in a
manner responsive to the supplementary air quantity ((a), (c) and
(d) of FIG. 17).
Next, in addition to the switching-on and -off of the first
electrical device 18, let it now be assumed that the air
conditioner is switched on at a time between the generation of the
TDC pulse 4 and the generation of the TDC pulse 5, and it is
switched off at a time between the generation of the TDC pulse 10
and the generation of the TDC pulse 11 ((b) of FIG. 17). The same
setting as that referred to previously is applied to the counts in
the counters CP1, NP1, CM1 and NM1 related to the first electrical
device 18 with respect to each of the TDC pulses ((c) of FIG.
17).
When the air conditioner is switched on, the switch 15 in FIG. 1
operatively connected thereto is closed to cause the supply of a
signal indicative of the on-state of the air conditioner to the ECU
9, and simultaneously the second control valve 30 is opened to
start supply of an increased quantity of supplementary air
responsive to the load on the engine increased by the air
conditioner. As previously described with respect to the first
electrical device 18, this increased supplementary air quantity is
actually sucked into an engine cylinder only after generation of
the TDC pulse 7 with a delay of two TDC pulses after the opening of
the second control valve 30 (immediately after the generation of
the TDC pulse 5 in FIG. 17) in the example of (e) of FIG. 17, due
to the suction lag attributed to the passage configuration and size
of the intake system between the second control valve 30 and the
engine cylinder, etc. Since there is no need of increasing the fuel
supply quantity until after the period corresponding to this
suction lag or the fuel increase-delaying period lapses, the count
in a counter CP4 in the ECU 9 is set to a predetermined value 2
immediately after the generation of the TDC pulse 5, and thereafter
this count is reduced by 1 at each of the following TDC pulses.
When the count in the counter CP4 is reduced to zero, the count in
a counter NP4 is set to a predetermined value, 5 for instance,
which corresponds to the fuel increasing period dependent upon the
load of the air conditioner. Upon inputting of each TDC pulse, this
count is reduced by 1. When the air conditioner is switched off at
a time between the generation of the TDC pulse 10 and the
generation of the TDC pulse 11, the switch 15 is accordingly closed
to cause the second control valve 30 to interrupt the supply of
supplementary air to the engine 1. A substantial reduction in the
supplementary air quantity occurs due to the above interruption of
the supply of supplementary air only after generation of two TDC
pulses, i.e. after generation of the TDC pulse 13. To count the
period corresponding to this suction time lag, i.e. the fuel
decrease-delaying period, the count in a counter CM4 in the ECU 9
is set to a predetermined value 2 at a time immediately after
generation of the TDC pulse 11 ((b) and (e) of FIG. 17). Upon
inputting of each of the following TDC pulses, the count in the
counter CM4 is reduced by 1 and when the count is reduced to zero,
the fuel decrease-delaying period terminates. To count the fuel
decreasing period, the count in the counter NM4 in the ECU 9 is set
to a predetermined value, 5 for instance, which is dependent upon
the magnitude of the load of the air conditioner on the engine,
followed by reducing the count by 1 at each of the following TDC
pulses ((e) of FIG. 17).
In (f) of FIG. 17, the symbol .SIGMA.NPi represents a sum of the
counts in the counter NP1 related to the first electrical device 18
and the counter NP4 related to the air conditioner occurring at
each of the TDC pulses, and the symbol .SIGMA.NMi a sum of the
counts in the counters NM1 and NM4 occurring at each of the TDC
pulses.
As previously noted, the fuel increasing periods dependent upon the
respective electrical loads of the first electrical device 18 and
the air conditioner last as long as the counts in the respective
counters NP1 and NP2 are other than zero. That is, the fuel
increasing period dependent upon the combined load of the first
electrical device 18 and the air conditioner lasts as long as the
sum .SIGMA.NPi of the counts in the counters NP1 and NP2 is other
than zero. Therefore, at each TDC pulse, this sum .SIGMA.NPi is
determined, and as long as the determined value assumes a value
other than zero, the valve opening period TIOUT of the fuel
injection valve 10 is calculated by the use of equation (1) to
increase the fuel quantity by the amount TAICP ((f) and (g) of FIG.
17).
Similarly, the sum .SIGMA.NMi occurring at each TDC pulse
determines the fuel decreasing period dependent upon the combined
load of the first electrical device 18 and the air conditioner. As
long as the sum .SIGMA.NMi assumes a value other than zero, the
valve opening period TIOUT of the fuel injection valve 10 is
calculated by the use of the equation (4) to decrease the fuel
quantity by an amount corresponding to the predetermined period
TAICM ((f) and (g) of FIG. 17).
In (f) of FIG. 17, the sum .SIGMA.NPi assumes a value of 1 and the
sum .SIGMA.NMi a value of 3, respectively, at a time immediately
after the generation of the TDC pulse 11. That is, the both sums
assume values other than zero. On such an occasion, the fuel
increase is preferentially effected to prevent engine stall, by
setting the value TAIC to TAICP in the equation (4) to increase the
fuel quantity by an amount corresponding to the predetermined
period TAICP.
Further, it is noted in (f) of FIG. 17 that the counts in the
counters NP1 and NP4 are both other than zero at a time immediately
after the generation of the TDC pulse 7. Even in such event, the
total fuel increasing amount is just an amount corresponding to the
single predetermined period TAICP. Likewise, the counts in the
counters NMl and NM4 are both other than zero at a time immediately
after the generation of the TDC pulse 13, and also on such an
occasion, the fuel decreasing amount is limited to an amount
corresponding to the single predetermined period TAICM. This is
because even if the supply quantity of supplementary air is
increased as multiple loads are applied to the engine, the actual
correcting amount required for compensation for the detection lag
of the absolute pressure sensor 12 is nearly constant irrespective
of the magnitude of the intake air quantity as shown in (a) of FIG.
17.
Although the foregoing explanations with reference to FIG. 17 are
based upon the assumption that only the first electrical device 18
and the air conditioner are switched on and off, similar
explanations may be applied also in the case where additional loads
are applied to the engine 1, such as those of the second and third
electrical devices 19 and 20, and the automatic transmission,
description of which is therefore omitted.
In the above described manner, when there occurs a sudden change in
the supplementary air quantity during the feedback control of
idling rpm, that is, when the engine is during the fuel increasing
period or during the fuel decreasing period, previously explained
with reference to FIG. 17, the predetermined value TAIC is added to
or subtracted from the aforementioned calculated value Ti as a
value corresponding to an amount of deviation from the required
fuel quantity mainly attributed to the detection lag of the
absolute pressure sensor 12, thereby supplying the engine 1 with a
proper amount of fuel fully corresponding to a change in the
supplementary air quantity, so as to maintain the air/fuel ratio of
the mixture being supplied to the engine at a theoretical value,
for instance.
Full Opening Mode Control after Engine Cranking
Next, the manner of controlling the first control valve 6 in full
opening mode immediately after completion of engine cranking
according to the invention, shown as steps 3 through 7 in (a) of
FIG. 6, will now be described.
When the answer to the question of the step 3 in (a) of FIG. 6
becomes negative for the first time after the start of the engine,
that is, when the engine rpm Ne becomes higher than the cranking
rpm NeCR for the first time after the start of the engine, then the
step 6 is executed only on condition that an affirmative answer is
obtained that the engine was cranking in the preceding loop, at the
step 5. In this step 6, the period of time tIU during which the
supplementary air is to be supplied to the engine in full opening
mode continuously from the termination of engine cranking, is
determined as function of engine cooling water temperature, for
instance, in accordance with the engine temperature-value tIU
relationship of FIG. 18. In (a) of FIG. 6, it is determined at the
step 7 whether or not the determined period of time tIU has passed
from the termination of the engine cranking. The duty factor for
the valve opening period of the first control valve 6 is maintained
at 100 percent after the termination of the engine cranking until
the period of time tIU lapses.
In the example of FIG. 18, the value tIU is set to and maintained
at a fixed value tIU0 (e.g. 5 seconds) below a predetermined value
TWIU1 (e.g. 40.degree. C.) of the engine cooling water temperature
TW. As the engine cooling water temperature increases, the period
of time tIU is stepwise reduced. During the idling operation, the
engine rpm is maintained at a value higher than the desired idling
rpm, by thus supplying supplementary air to the engine in full
opening mode even after the termination of engine cranking for a
suitable period of time tIU, thereby avoiding unstable rotation of
the engine due to the operation of the dynamo or generator of the
engine for charging the battery. Further, since the idling rpm is
set to higher values as the engine temperature becomes lower, the
temperature of the engine cylinder wall can be promptly increased
by the increase of idling engine rpm dependent upon the engine
temperature to achieve stable combustion within the engine
cylinders.
Further, in the event of presence of bubbles in the feeding pipes
of the fuel feeding system, which makes the idling operation
unstable and will occur in a high temperature atmosphere, for
instance, when the engine cooling water temperature is higher than
a predetermined value TWIU3, e.g. 80.degree. C., the full opening
period of time tIU is set to a value tIU3 which is rather large,
for instance, 4 seconds, at engine idle, thereby removing the
bubbles promptly for stable rotation of the engine.
Although according to the example of FIG. 18, the period of time
tIU is varied in a stepwise manner with respect to a change in the
engine cooling water temperature, the functional relationship
between the value tIU and the engine cooling water temperature is
not limited to that of the illustrated example, but it may vary
depending upon the operating characteristics of the engine
concerned, for instance, the period of time tIU may be linearly
varied as a function of the engine cooling water temperature.
Next, the electrical circuit within the ECU 9 will now be explained
by referring to FIG. 19 illustrating the same circuit by way of
example.
The engine rpm sensor 14 in FIG. 1 is connected to an input
terminal 902a of a one chip CPU (hereinafter merely called "CPU")
902 by way of a waveform shaper 901, and also to a group of input
terminals 903a of a fuel supply control unit 903, all provided
within the ECU 9. Reference numerals 18', 19' and 20' designate
sensor means for detecting the electrical loads of the electrical
devices 18, 19 and 20 in FIG. 1, which are connected to respective
ones of a group of further input terminals 902b of the CPU 902 by
way of a level shifter unit 904 in the ECU 9. Further, the switches
15 and 16 are connected to the above input terminals 902b of the
CPU 902 by way of the level shifter unit 904. The water temperature
sensor 13 and the throttle valve opening sensor 17 are connected,
respectively, to input terminals 905a and 905b of an
analog-to-digital converter 905 and are also both connected to the
input terminals 903a of the fuel supply control unit 903. The
analog-to-digital converter 905 has an output terminal 905c
connected to the input terminals 902b of the CPU 902 and a group of
further input terminals 905d connected to a group of output
terminals 902c of the CPU 902. A pulse generator 906 is connected
to another input terminal 902d of the CPU 902 which in turn has an
output terminal 902e connected to AND circuits 908 and 912 at their
one input terminals, by way of a frequency divider 907. The AND
circuit 908 has its output connected to a clock pulse input
terminal CK of a first down counter 909. The AND circuit 908 has
its other input terminal connected to a borrow output terminal B of
the first down counter 909 which terminal is further connected to a
load input terminal L of a second down counter 913 by way of a one
shot circuit 911. The first down counter 909 has its load input
terminal L connected to a first one of another group of output
terminals 902f of the CPU 902. The above first one output terminal
is also connected to another group of input terminals 903b of the
fuel supply control unit 903. The AND circuit 912 has its output
connected to a clock pulse input terminal CK of the second down
counter 913, and its other input terminal to a borrow output
terminal B of the same counter 913, respectively. The borrow output
terminal B of the second down counter 913 is also connected to the
solenoid 6a of the control valve 6 in FIG. 1 by way of a solenoid
driving circuit 915. A second one of the output terminals 902f of
the CPU 902 is connected to an input terminal 914a of a first
register 914 which in turn has its output terminal 914c connected
to an input terminal 913a of the second down counter 913. Another
one of the output terminals 902f of the CPU 902 is connected to the
input terminal 910 of the second register 910 which has its output
terminal 910c connected to the group of input terminals 903b of the
fuel supply control unit 903.
The analog-to-digital converter 905, the CPU 902, the first
register 914, the second register 910 and the first down counter
909 are connected together by way of a data bus 916, respectively,
at an output terminal 905e, an input and output terminal 902g, an
input terminal 914b, an input terminal 910b, and an input terminal
909a.
Connected to the input of the fuel supply control unit 903 are the
intake air pressure or absolute pressure sensor 12 and the other
engine parameter sensor 25 such as an atmospheric pressure sensor,
all appearing in FIG. 1. The output terminal 903c of the fuel
supply control unit 903 is connected to the fuel injection valve 10
in FIG. 1.
The electrical circuit of the ECU 9 constructed above operates as
follows: An output signal from the engine rpm sensor 14 is supplied
to the ECU 9 as a signal indicative of engine rpm Ne as well as a
signal indicative of a top dead center of the engine 1, where it is
subjected to waveform shaping by the waveform shaper 901 and then
supplied to the CPU 902 and the fuel supply control unit 903. The
CPU 902 is responsive to each pulse of the TDC-synchronous signal
to generate and supply a chip selecting signal, a channel selecting
signal, an analog-to-digital conversion starting signal, etc. to
the analog-to-digital converter 905, commanding the latter to
convert analog signals such as the engine cooling water temperature
signal and the throttle valve opening signal from the cooling water
temperature sensor 13 and the throttle valve opening sensor 17 into
corresponding digital signals. When the A/D converter 905 generates
through its output terminal 905c a signal indicative of completion
of the analog-to-digital conversion of one of the analog signal,
the digitally converted signal indicative of engine cooling water
temperature or throttle valve opening is supplied as a data signal
to the CPU 902 via a data bus 916. Upon completion inputting of one
of such digitally converted signals to the CPU 902, the same
process as above is repeated to cause inputting of the other
digitally converted signal to the CPU 902. Further, load-indicative
signals from the electrical load sensor means 18', 19' and 20' and
on-off state signals from the switches 15 and 16 are supplied to
the CPU 902 after having their levels shifted to a predetermined
level by the level shifter unit 904.
The CPU 902 operates on input data signals, that is, the engine rpm
signal, the electrical load signals, the mechanical load signals,
the engine water temperature signal and the throttle valve opening
signal to first determine operating conditions of the engine. More
specifically, as previously stated, the CPU 902 determines that the
engine should be operating in full opening mode when the engine rpm
Ne indicated by the engine rpm signal is smaller than the cranking
rpm NeCR and also when the period of time tIU does not yet lapse
after the engine rpm Ne has exceeded the cranking rpm NeCR, and the
engine should be operating in decelerating mode when the throttle
valve opening signal shows a value indicative of the full closing
of the throttle valve and simultaneously the engine rpm Ne
indicated by the engine rpm signal shows a value smaller than the
predetermined rpm NA, respectively. Responsive to the results of
the above determination, the CPU 902 calculates the valve opening
delaying period of time TDLY and the valve opening period TOUT for
the first control valve 6, and the value TAIC in the equation (4)
for the fuel injection valve 10.
The manner of calculating the above periods TDLY, TOUT will now be
described in detail with reference to FIG. 20. In FIG. 20, when an
nth pulse of the TDC signal is inputted to the CPU 902, operations
are carried out within a period of time Ts from the above inputting
of the TDC signal pulse, which include reading of the
aforementioned data signals into the CPU 902, arithmetic
calculations of the valve opening delaying period TDLY and valve
opening period TOUT of the first control valve 6 and supply of the
resulting calculated values from the CPU 902 to the first down
counter 909 and the first register 914. After these operations are
over, the first control valve 6 is opened upon a lapse of the
calculated valve opening delaying period TDLY for the calculated
period of time TOUT. As noted above, exactly saying, the valve
opening delaying period applied after the inputting of each TDC
signal pulse is equal to Ts+TDLY. The period Ts consisting of the
data reading period and the arithmetic calculating period has a
nearly constant value and is applied upon inputting of each pulse
of the TDC signal to the CPU 902 at substantially constant
intervals of time. Therefore, the valve opening delaying period
TDLY alone is calculated upon inputting of each pulse of the TDC
signal.
The valve opening delaying period TDLY and the valve opening period
TOUT can be determined by the following equations:
In the above equations, Men represents a time interval from
inputting of an (n-1)th pulse of the TDC signal to inputting of the
nth pulse of same, and the value of Me is inversely proportional to
the engine rpm Ne, that is, it decreases as the engine rpm Ne
increases. As expressed by the equations (5) and (6), the valve
opening delaying period TDLY and the valve opening period TOUT are
determined by multiplying the value of Me by constants DDLY and
duty factor DOUT (in percentage), respectively. Although the
calculations of the values TDLY and TOUT applicable after inputting
of the present nth pulse of the TDC signal should be made by using
the corresponding time interval Men+1 to obtain exact calculated
values, the value of Men+1 is not yet known at the time of
calculating the present values TDLY and TOUT and the value Men+1 is
nearly equal to the value of Men applied in the previous loop.
Therefore, the value of Men is used for calculating the values TDLY
and TOUT.
In the equation (5), as previously stated, the coefficient DDLY is
a constant which has its value dependent upon the configuration of
the intake pipe of an engine applied, etc. and experimentally
determined for each engine applied. It is set at a value so as to
make the phase of the fluctuating cycle of the intake pipe absolute
pressure always constant with respect to generation of each pulse
of the TDC signal, for instance, it is set at 25 percent.
In the equation (6), as previously stated, the duty factor DOUT is
a variable which has its value determined upon inputting of each
pulse of the TDC signal and as a function of engine rpm, engine
cooling water temperature, electrical loads, etc. It is set to
appropriate values so as to control the idling rpm to a value
appropriate for the engine load at idle. To is a constant
representing a dead period of time corresponding to the response
lag of the first control valve 6, or a like factor, and is set at 7
ms, for instance.
During full opening mode control according to the invention, the
duty factor DOUT is set to 100 percent, that is, the first control
valve 6 is continuously opened during full opening mode control.
More specifically, as indicated by the broken line in FIG. 20, the
control valve 6 is kept opened even after generation of an (n+1)th
TDC pulse until the determined period of time tIU lapses.
Data indicative of the values TDLY and TOUT calculated by the
equations (5) and (6) are generated from the CPU 902 and loaded
into the first down counter 909 through the data bus 916 upon
inputting of a reading command signal to their input terminals 909a
and 914a. That is, the valve opening delaying period TDLY is loaded
into the first down counter 909, and the valve opening period TOUT
into the first register 914, respectively.
Clock pulses generated by the pulse generator 906 are used as a
reference signal for control of the operation of the CPU 902, while
they are subjected to frequency division into a suitable frequency
by the frequency divider 907, and then applied to the AND circuits
908 and 912 at their one input terminals.
The CPU 902 applies a starting command signal to the first down
counter 909 at its load input terminal L upon the lapse of the
period Ts after inputting of each pulse of the TDC signal to the
CPU 902. Upon being supplied with this starting command signal, the
first down counter 909 is loaded with the calculated valve opening
delaying period value TDLY and at the same time generates a high
level output of 1 at its borrow output terminal B and applies it to
the AND circuit 908 at its other input terminal.
As long as the AND circuit 908 has its other input terminal
supplied with the above high level output of 1, it allows clock
pulses applied to its one input terminal to be applied to the first
down counter 909 at its clock pulse input terminal CK. The first
down counter 909 counts clock pulses until the count reaches a
value corresponding to the calculated value of the valve opening
delaying period TDLY for the first control valve 6. Upon counting
the above value, the first down counter 909 generates a low level
output of 0 through its borrow output terminal B to close the AND
circuit 908 to cause interruption of application of clock pulses to
the first down counter 909.
The one shot circuit 911 applies a starting command pulse to the
second down counter 913 at its load input terminal L each time it
is supplied with the above low level output from the first down
counter 909. That is, the above starting command pulse is applied
to the second down counter 913 upon completion of the counting of
clock pulses corresponding in number to the calculated valve
opening delaying period TDLY by the first down counter 909.
Upon being supplied with the starting command pulse from the one
shot circuit 911, the second down counter 913 is loaded with the
calculated valve opening period value TOUT from the first register
914, and at the same time generates a high level output of 1 at its
borrow output terminal B and applies it to the AND circuit 912 at
its other input terminal and also to the solenoid driving circuit
915. The solenoid driving circuit 915 operates to cause
energization of the solenoid 6a of the first control valve 6 in
FIG. 1 for supply of supplementary air to the engine 1 as long as
it is supplied with the above high level signal of 1 from the
second down counter 913.
While the AND circuit 912 has its other input terminal supplied
with the high level signal of 1, it allows clock pulses applied to
its one input terminal to be applied to the clock pulse input
terminal CK of the second down counter 913. In a manner similar to
the operation of the first down counter 909, the second down
counter 913 continuously generates a high level ouput of 1 through
its borrow output terminal B until it is supplied with clock pulses
corresponding in number to the calculated valve opening period
TOUT, and upon counting clock pulses corresponding in number to the
value TOUT, it generates a low level output of 0 through the same
terminal B to cause the solenoid driving circuit 915 to deenergize
the solenoid 6a of the first control valve 6. At the same time, the
above low level output of the second down counter 913 is also
supplied to the AND circuit 912 to interrupt the application of
clock pulses to the second down counter 913.
As is often the case with the full opening mode control according
to the invention where the duty factor DOUT is set to 100 percent,
for instance, the phenomenon can take place that before a counting
of the valve opening period TOUT is terminated in the second down
counter 913, a next starting command signal from the first down
counter is applied to the load input terminal L of the second down
counter 913 through the one shot circuit 911. In such event, the
second down counter 913, upon being supplied at its load input
terminal L with the above next starting command signal, gets loaded
with a new calculated and stored value of the valve opening period
TOUT from the first register 914 to start counting a number of
clock pulses corresponding to the newly loaded value. Therefore, in
such event, the solenoid 6a of the first control valve 6 is kept
energized by means of the solenoid driving circuit 915, that is,
kept in its fully opened state.
On the other hand, the value TAIC in the equation (4), calculated
by the CPU 902, is supplied to the second register 910 through the
data bus 916, upon a loading command signal being applied to its
input terminal 910a from the CPU 902.
On the other hand, the fuel supply control unit 903 operates on
engine operation parameter signals supplied from the engine rpm
sensor 14, the engine water temperature sensor 13, the throttle
valve opening sensor 17, the absolute pressure sensor 12, and the
other engine operation parameter sensors 25, which are sequentially
supplied to the same unit 903 in synchronism with the TDC signal,
to calculate a desired value of the valve opening period Ti in
accordance with the equation (1), upon inputting of each TDC pulse
to the unit 903. The starting command signal So, which is supplied
to the first down counter 909, is also supplied to the fuel supply
control unit 903 to cause inputting of the calculated value TAIC
stored in the second register 910 thereto. The above command signal
So also causes the fuel supply control unit 903 to calculate a
value of the valve opening period TIOUT by adding the input value
TAIC to the above calculated value Ti, to cause the fuel injection
valve 10 to open for the calculated valve opening period.
Although the foregoing embodiment is directed to an internal
combustion engine equipped with an automatic transmission, the
method of the invention may of course be applied to an internal
combustion engine equipped with a manual transmission, providing
the same results as described above.
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